746 Hiley . — ( 9 # the Value of Different Degrees of 
These results are summed up in the following table : 
Table II. 
Helianthus annuus radicles. Temp. = 20°-25° C. 
Results with long total periods (i. e. 20 m. and upwards). 
No. of 
C 
t 
CT 
Exp. 
mg 
T 
( i + T ) 
mg.t 
h. 
m. 
s. 
19 
< 8*46 
3 * 12 
1 
0 
0 
< 2-71 
20 
13-1 
7 -i 4 
1 
0 
0 
1-83 
21 
14-9 
5*04 
40 
30 
2-96 
22 
15.0 
8-92 
20 
0 
i-68 
23 
> 16-19 
8-84 
1 
0 
0 
> 1-83 
24 
16-22 
3 *i 6 
1 
0 
0 
5 -i 3 
25 
> 168 
6-o 
1 
0 
0 
> 2-8 
26 
17-2 
6-n 
4 i 
0 
2-82 
27 
> 17-2 
9-°5 
40 
30 
> 1-90 
28 
> 17*54 
7-07 
1 
0 
0 
> 2-48 
29 
18-8 
(0 11,11 
40 
30 
> i '7 (?) 
By comparing the results in Tables I and II it will be seen that 
though the equation holds good when the total period is less than 16 min., 
yet CT > mg. t. when the total period is greater than 19 min. This 
discrepancy was the cause of much confusion in the interpretation of 
earlier results. It is not easy to understand why, though a radicle grows 
straight under the influence of alternating stimuli of 10 mg. for 1 min. and 
1 mg. for 10 min. in opposite directions, it does not grow straight under 
alternating and opposite stimuli of 10 mg. for 3 min. and 1 mg. for 30 min. ; 
yet such is undoubtedly the case. It was thought that some light might be 
thrown on these results if it were found that the presentation time for 
Helianthus radicles was more than 16 min. and less than 20 min., as 
in that case a critical time would be passed in the later experiments. But 
experiments were carried out to determine the presentation time of 
Sunflower radicles, and these show that this time is less than five minutes. 
Presentation Time for Radicles of Helianthus annuus . 
This value was determined in the following way. Seedlings were 
grown in a pan of damp sand in the experimenting room which was kept at 
a temperature of 18 to 20° C. They thus remained at the same temperature 
from the beginning of germination till the end of the experiment. When 
the radicles were 5 to 15 mm. long, the seedlings were taken out, carefully 
washed in water at the temperature of the room, and pinned to squared 
corks covered with wet blotting-paper. The corks were pushed on to the 
